This highly engaging analysis of the contemporary, global social and political landscape of trans antagonisms draws specific attention to "gender-critical" mobilizations of Simone de Beauvoir's account of becoming a woman in The Second Sex to advance and justify trans exclusionary positions. Through a careful examination and application of Beauvoir's philosophical and political commitments, Becoming a Woman compellingly explores the significance of her notion of becoming as not only affirmative of trans women, but also as an ethical demand to affirm trans possibilities. More than a reply to gender-critical readings of Beauvoir, this book develops an original, Beauvoirian ethics of gender affirmation offering that show why we ought to challenge trans exclusion and anti-trans movements.